Twin turbo efficency range -How do I work it out?

[Mr Ed]

Im in the early stages of planning a twin turbo upgrade for later in the year(if all goes to plan)

After reading some comments in the Chinese turbo thread its got me thinking about boost levels.........if a turbo is efficient for upto 20psi on its own, am I am able to run higher boost with twins? I know I obviously can but I dont know the theory behind it.

How do I work out the efficiency range of a twin setup knowing the specs of each individual turbo??

[ViPeR_NiPPleX]

if the turbos are equal, just assume half the exhaust gasses are going to one.. so on a 1jz, treat is as a 1250cc 3 cylinder. I'm assuming that's kinda how it works ??

[Hen]

Efficiency of a turbo depends on both boost pressure and airflow. So with twins, you'll be looking at the same boost pressure but only half the airflow when compared to a single.

If you take a look at any compressor map you'll see how this changes things.

And I also agree with Viper.

Hen

[thechuckster]

hopefully not too dumb suggestion: see what people are doing with Starlets for turbos - do the same but twice?

[Bored?]

I assume that you mean two turbos running in parallel. In that case, take the compressor map for one turbo, and then double all the numbers on the horizontal (flow) axis. (ie. stretch the horizontal axis).

If in series (rare for cars), double the vertical (pressure ratio) axis.

So the answer is that no, two turbos will not increase the maximum boost at which they are efficient.

If the compressor map for your (paralleled) turbo of choice doesn't go high enough, you're probably better off with a larger turbo with more flow, since maximum boost pressures tend to increase with the compressor wheel diameter, such that big turbos often have maps which look like they're stretched vertically.

So, for example, twin GT40R's flow similar to a GT5533R, but the GT5533R would be better if you needed higher pressures, while the twin GT40R's might be better if you didn't.

[ReQuieM]

It's funny how every one thinks more boost equals more power. Its kinda all about CFM. More air more power. Thats where twins come into their own. I've got an awesome book here on turbo thiery and application call 'turbochargers' from HP books. Tells you every thing you need to know.

If possible don't go by HP levels or maximum PSI, go by the compressor map. It's all about efficiency range.

[ReQuieM]

Whoops just re-read your first post. Just do what you do on one lot just half the engine when you do it